Continuous propane dewaxing



July 25, 1939. E. w. THIELE 2,167,340

CONTINUOUS PROPANE DEWAXING Filed Dec. 50, 1936 81/265 DRUM INVENTORIErnesf W Th/e/e PRO/ ANE ATTORNEY WMW Patented July 25, 1939 UNITEDSTATES CONTINUOUS PROPANE DEWAXIN G Ernest w. Thiele,

Chicago, 111., assignor to Standard Oil Company, Chicago, 111., acorporation of Indiana ApplicationDecember 30, 1936, Serial No. 118,383

2 Claims.

This invention relates to the separation of wax from oil andparticularly to the separation of paramn wax from mineral oil by the useof a liquefledmormally gaseous diluent, such as propane, and it relatesmore particularly to a new and improved apparatus for carrying out thisseparation in-a continuous manner.

It has been found that propane and other liquefied normally gaseousdiluents, such as have been devised for the elimination of this I shookchilling eifect.

due type of apparatus heretofore proposed comprises a number of flashdrums arranged in 25 series, each two adjacent flash drums being connected by a single pipe containing a valve. The pressure drop necessaryto accomplish the selfrefrigeration takes place almost exclusivelyacross the valves and even though the chilling is con- 30 ducted inseveral steps by reason of the number of flash drums, serious shockchilling ensues. It has been proposed in Atwell Patent 2,006,011 toeliminate this difficulty by' the use of a long restricted pipe giving agradual pressure drop. My

35 invention relates to a more practical, flexible and eilicientapparatus for carrying out the method of the Atwell patent.

It is an object of my invention to provide a propane dewaxingapparatus-which will be highly eflicient and highly flexible, which willpermit continuous operation and which will eliminate the difficultiesinherent in flash chilling. Further and more detailed objects of myinvention will become apparent as the description thereof proceeds.

The invention will be described with particular reference to a preferredembodiment thereof which is given by way of illustration and not by wayof limitation. Various modifications will be 50 apparent to thosesldlled in the art and are within the scope of my invention.

This preferred embodiment is illustrated in the accompanying drawingwhich forms a part of this specification and which shows my ap- 5paratus diagrammatically.

Referring nowm "'re;.particularly to the draw ing,'propane or otheliquefled normally gaseous diluent fromstorage tank ll passes therefromthrough pump l2 and a combined heater and go mixer ll. Simultaneously,the oil to be dewaxed increases the flexibility of the apparatus.

is pumped from storagetank It by pump I5 into heater and mixer I!wherein it is brought into solution in the propane, preferably at atemperature above that at which the wax is completelysoluble. solutionpasses preferably to a'surge drum l6 and then throughv one or more of agroup of inde-- pendent, long, restricted conduits C1 arranged inparallel with each other. In these long restricted conduits there is agradual pressure drop 10 which results .in a gradual and continuousvaporization of propane and gradual andcontinuous chilling. The parallelconduits C1 discharge into a drum 1'! from which the propane vaporsliberated during the passage of the solution through the conduits C1 areremoved passing overhead through valve is and line l9 'to a compressorand condenser}! and thus back to the storage tank II. I prefer to use atleast three conduitsr arranged in parallel. 0

Each of the long restricted conduits C1 is equipped with a valve V1. Anyone of these valves is always either open or closednever throttled. Inother words, there is no sudden pressure drop across a valve since thiswould result in the undesirable flash chilling effect previouslymentioned. In order to produce a more or less uniform rate of chillingduring the pas-- sage of the mix through the pipe, it will generally befound desirable to form each conduit of several sizes of pipe,increasing in diameter toward the exit end of the conduit.

By using a number of long restricted pipes in parallel, flexibility issecured and this flexibility is extremely important. At any given timeone, two or any number of these pipes can be used, the remainder, ifany, being shut off by the ap- I propriate valves. It is highlydesirable, although not completely necessary, that theseconduits bedifierent in size from each other since this greatly.

Thus, for instance, if the first conduit C1 has a capacity taken asunity, the second conduit C1 can have a capacity of two units, the thirdconduit C1'a capacity of four units, the fourth conduit C1 a capacity of8 units and the fifth conduit C1 a capacity of 16 units. With thisarrangement it will be seen that by control of the various valves V1 anyj given valve being either completely open or cornpletely closed,thirty-one different capacities are available. In other words, the totalcapacity of the conduit system connecting surge drum i6 and drum II canbeany integral number of units from one to 31. Y

' While the various conduits C1 can all be of the same length, it ispreferred to apportion the I lengths and diameters of the variousconduits so that the course of the fall of the temperature and pressurethrough them will be the same. -More-" over, it is desirable that thetime which it takes From the heater andmixer I3 the 5- the mix to travelthrough each of the parallel conduits be the same, since the timedetermines the rapidity of crystallization, which in turn determines(with other factors) the character of the crystals. These conditions arefulfilled when the following relationships hold:

where d is the diameter of the conduit, 1 its length, 12 its capacity,and In and k: are constants. It follows from these equations that:

l=k3d or, in other words that the length varies with the cube root ofthe diameter. Thus if one of conduits C1 has adiameter eight times asgreat-as that of a second of conduits C1 (to take a very extreme case)it should be twice as long and would have 128 times the capacity of thesecond conduit.

These considerations hold even when each conduit increases in sizetoward the exit end since the capacity is thesame throughout theconduit. In this case, the diameter relationships referred to in thepreceding paragraph must be taken in terms of diameters at correspondingpoints on the various conduits.

The liquid material from drum El carrying some wax in suspension passesthrough a second conduit system composed of conduits C2, similar toconduits C1 of the first conduit system, connecting surge drum l6 anddrum H. The second conduit system discharges into drum 22, preferablybelow the liquid level therein.

I have illustrated an apparatus having two conduit systems and twodischarge drums, i. e.

two stages. It will,.however, be understood that any number of stagescan be used and in actual practice I prefer to use at least five orsix'sets of conduit systems and discharge drums, i. e. at least five orsix stages, in order to permit the gradual removal of the liberatedpropane vapors. Otherwise the system tends to become loaded up withvapors and the capacity of the conduit systems is decreased.

Returning to drum 22 it will-be seen that propane vapors are againremoved overhead passing through valve 23, line 26, compressor 25 andcondenser 21 back to storage tank H. This compressor can be made largeenough to take care of the vapors from drum H by opening valve 26 andpassing them through the by-pass line 21 into line 2d. In this casecompressor 20 can be shut down or eliminated. The liquid from the lastdrum, carrying wax in suspension, passes through line 28 to awax removaldevice or wax removal devices which may be filters, settlers orcentrifuges. I prefer to use one or more continuous filters 29. Wax iscontinuously discharged from continuous filter 29 through'line 39 andfreed from propane by means not shown. The filtrate from continuousfilter 29 is passed to a recovery system by means of pump 3!. Preferablyits capacity to absorb heat is utilized in the system. This can be doneby passing the cold filtrate through a line 32 to a heat exchanger coil33 arranged in the vapor space above drum 22. This serves to recondensesome of the propane vapors and is equivalent to the introduction ofadditional cold propane into drum 22 to make up for the evaporation inconduits C2. It is also possible, of course, to introduce makeup propanefrom storage tank H by means not shown. The filtrate then passes throughline 34 to a second heat exchange coil 35 in the vapor space above druml1 and thence through line 36 and heater 3! to still 38, which ispreferably operated under considerable pressure. From the still, propanevapors pass to condenser 2| and back to storage tank II. The oil, atleast partially freed from propane, passes out of the bottom of still 38through valve 39. In accordance with common practice still 38 isoperated at a pressure of several hundred pounds per square inch vinorder to avoid recompression of the propane vapors. This results in theremoval of some residual propane along with the oil through valve 39 andthis can be removed by flashing and stripping in the conventionalmanner, but this is not shown.

The liquid levels in drums I1 and 22 are controlled by liquid levelcontrollers 40 and M acting'on valves l8 and 23 respectively.

It will be understood that in a propane dewaxing system there are agreat many variables which make it highly desirable to have the utmostpossible flexibility. Various Wax bearing lubricating oil stocks arehandled from time to time, various changes in the diluent compositionare encountered, changes in the ratio of oil to diluent may becomedesirable, etc. Furthermore, in the actual operation of the system evenwith a fixed stock, a fixed diluent, a fixed diluent to stock ratio,etc. it becomes necessary to adjust the systern from time to time inorder to keep the various stages operating at the same rate and toproduce the desired amount of cooling in each stage. This .fiexibilityis completely lacking in apparatus of this type heretofore known.

. While I prefer to do all my chilling in apparatus of the typedescribed, it will be understood that a portion of the chilling can beconducted in other types of apparatus, for instance, by indirect heatexchange in scraped surface chillers. The more critical portion of thecooling operation should be conducted in the apparatus of my invention.

I claim:

1. Apparatus for dewaxing a wax-bearing mineral oil by the use of. aliquefied normally gaseou hydrocarbon diluent, comprising means fordissolving said oil in said diluent, a plurality of friction-dropchilling stages to precipitate wax from said oil and means for removingthe precipitated wax from the oil, each of said frictiondrop chillingstages comprising a plurality of independent, long, restricted conduitsadapted to accomplish friction-drop chilling and arranged in parallelwith each other, said parallel conduits being of substantially differentcapacities, the larger of said conduits being relatively long and thesmaller of said conduits being relatively short, shut-off valves topermit the selective use of any one or more of said parallel conduits, avessel into which said conduits discharge, and means for removingdiluent vapors from said vessel.

2. Apparatus according to claim 1 in which the respective lengths ofsaid conduits are approximately proportional to the cube roots of their.

respective diameters at corresponding points.

ERNEST W. THIELE.

